Many imaging systems suffer from wave front aberrations, which reduce image quality and sharpness. Image quality, sharpness and signal to noise ratio can be improved by correcting actively for wave front aberrations in the optical system. Most adaptive optics schemes employ a device such as a shack-Hartmann sensor, to measure the wave front aberrations. Based on these measurements an active element like a deformable mirror or a spatial light modulator corrects the optical system for the wave front aberrations. Correction for wave front aberrations have been implemented in ophthalmic imaging, where the aberrations introduced by the cornea and lens are actively corrected for.
One example of adaptive optics in opthalmology is the implementation in a laser scanning opthalmoscope (SLO). In retinal imaging by a SLO an image of the retina is formed by raster scanning a focused beam over the retina and detection of the reflected light. To improve image quality, the out of focus light is rejected by a pinhole, in analogy to confocal microscopy. Adaptive optics has been implemented to reduce the aberrations by the cornea and lens. FIG. 1 shows a prior art implementation of adaptive optics in an SLO configuration that uses a Shack Hartman sensor to measure the wave front aberrations.
Another example is adaptive optics combined with Optical Coherence Tomography (OCT). In ophthalmic OCT, the light reflected from the retina is coupled back into a single mode fiber. The single mode fiber acts as a pinhole, accepting only one spatial beam mode. Ocular aberrations not only distort the beam profile on the retina, but also distort the beam profile of the reflected light from the retina. Due to the spatial filtering by the single mode fiber, a portion of the reflected light does not couple back into the fiber. An arrangement to address this issue may use of adaptive optics. Adaptive optics has been integrated with TD-OCT systems and procedures as described in Hermann, B. et al., “Adaptive-optics ultrahigh-resolution optical coherence tomography,”, Optics Letters, 2004. 29(18): pp. 2142-2144.
Due to reduced beam aberrations on the retina and improved coupling of the reflected light back into the single mode fiber, a signal-to-noise (SNR) improvement of up to 9 dB was demonstrated compared to the uncorrected case. It was also demonstrated that the main corrections were associated with defocus and astigmatism. (See Zawadzki, R. J. et al., “Adaptive-optics optical coherence tomography for high-resolution and high-speed 3D retinal in vivo imaging”, Optics Express, 2005. 13(21): pp. 8532-8546, FIG. 2). In other demonstrations of adaptive optics integrated with an SD-OCT system, an improvement in the SNR may have been attributed mainly to a correction for defocus and astigmatism as described in the Zawadzki publication referenced above, and an increase in SNR by 7 dB may have been achieved using adaptive optics as described in Zhang, Y. et al., “High-speed volumetric imaging of cone photoreceptors with adaptive optics spectral-domain optical coherence tomography”, Optics Express, 2006. 14(10): pp. 4380-4394. FIG. 1 herein shows a diagram of a conventional system having an SLO configuration with adaptive optics as also shown in A. Roorda, et al., “Adaptive optics scanning laser opthalmoscopy”, Opt. Express 10, pp. 405-412 (2002).
There may be a need to overcome certain deficiencies associated with the conventional arrangements and methods described above.